From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison of engine roughness and crankshaft stiffness for six-cylinder, straight-eight, and twin-six engines.
| Identifier | ExFiles\Box 23\5\ Scan076 | |
| Date | 1st February 1923 guessed | |
| contd :- -4- Other variables being omitted, in engines without dampers, the amplitude and severity of torsional vibration in the shaft at a critical period will vary directly as the disturbing torques and inversely as the crankshaft stiffness. In a report attached it is shewn that for the above three engines to have critical periods at the same speeds, the relative crankshaft stiffnesses must be : six-cyl. 1.0 straight-8 2.0 twin-six 1.2 So that a comparison of the roughness at the critical period of these engines will be as follows :- Ratio six-cyl. (246 + 87) X 1/1 = 333 6.9 straight-8 (64 + 33) X 1/2 = 48.5 1.0 twin-six 174 X 1/1.2 = 145 3.0 ----------- CRANKSHAFTS FOR STRAIGHT-EIGHT AND TWIN-SIX ENGINES. We have made rough calculations to shew the approximate stiffness that would be required in the crankshafts of the above types of engines, with cyls. like the 20 HP. These stiffnesses will be sufficient to keep the main crankshaft torsional period at the speed at which it is at present in the 20 HP. namely 3300 r.p.m. The stiffness of the standard crankshaft E.54064 is 16220 lbs.ft/radian. (1) Straight-eight engine. The main period in a 6-cyl. engine is the one where the shaft executes 3 vibrations contd :- | ||